The prior art is familiar with polarization rotators, which are for example useful in image enhancement, polarimetry and optical switching. The polarization rotator receives a beam of optical radiation with a first polarization state and produces a new coaxial beam with a second polarization state. One prior art polarization rotator employs an electrically-switchable half-wave plate that, when switched, converts the incoming beam at a first polarization state into an orthogonal state, for example rotating linearly polarized light by ninety degrees. Another prior art polarization rotator operates similarly but employs twisted nematic liquid crystal in an electrically-switched cell.
But prior art polarization rotators do not simultaneously provide sufficient switching speed over a broad spectral range. For example, prior art polarization rotators employing thick twisted nematic liquid crystals operate over a broad spectral range but have switching speeds limited to seconds. On the other hand, prior art polarization rotators employing a half-wave plate have switching speeds faster than 100 μs but have very limited spectral range. FIG. 1 illustrates the spectral range 10 of a prior art polarization rotator employing one half-wave plate for λ=550 nm, and the spectral range 12 of a prior art polarization rotator employing three half-wave plates for λ=550 nm. In FIG. 1, x-axis 14 represents wavelength and y-axis 16 represents percentage of 90 degree rotation of the polarization state.